Stereo pair displays are stereoscopic displays containing separate left eye and right eye images. These images are viewed by various techniques allowing each eye to separately perceive its associated image and thus, allow a viewer to perceive a single three dimensional image. One common technique for viewing stereo pair displays involves the use of left and right eye filters, such as red-blue filters or polarized filters. Stereo pairs may also be placed side by side and viewed without the aid of a viewing device by free viewing. Free viewing involves crossing ones vision or extending ones focal point beyond the page containing the stereo pair images such that each image of the stereo pair appears to overlap and create a single stereoscopic image.
One type of stereo pair image display includes random dot stereograms consisting of a pair of apparently random patterns of dots (pixels) that when viewed stereoscopically, produce a three dimensional image. In a random dot stereo pair, each image frame is devoid of monocular cues. This means that each image frame, by itself, is meaningless and retains no information specific to the stereoscopic image. Parallax differences are achieved between the right eye and left eye image frames by making slight horizontal shifts to the pixels comprising the random patterns. The left eye and right eye image patterns are identical, except for these pixel shifts. When free viewing or viewing using some type of stereoscopic filter or device, the pixel shifts between the images are taken as depth cues by the brain and causes the perception of depth by a viewer.
The inherent limitation of all stereo pair displays, including dual image random dot stereograms, is the failure of the displays to be autostereoscopic. Autostereoscopic displays are displays in which apparent depth can be perceived without the use of a viewing device. Viewing of stereo pair displays require viewing devices or requires complicated and often eye tiring free viewing of the images. Thus, an autostereoscopic display presents a simpler means for viewing stereoscopic images.
A lenticular screen display is one type of autostereoscopic display comprised of a flat rear surface containing a photographed or lithographically printed image composed of a number of interlaced source frames. A lenticular material consisting of a series of cylindrical lenses allows light to enter and be focused upon the flat rear surface. In a lenticular screen display, source frames generally contain images from progressive prospectives of an object or objects in the display. The source frames are interlaced into very fine alternating vertical strips and then compressed horizontally so that the resulting image is the width of a single one of the source frames.
A lenticular material is then placed over the resulting image. As the viewer perceives the display through the lenticular material, the left eye sees one group of strips corresponding to a first source frame through the lenses of the lenticular material, while the right eye sees a second group of strips corresponding to a second source frame through the lenses of the lenticular material. Depending on the viewing angle, the lenses focus the viewers left and right eyes on the interlaced strips of any two adjacent or closely related groups of source frames forming a stereo pair. As the viewer changes viewing angles, such as by walking in one direction across the front of the display, the stereo pair of source frames that the viewer sees through the lenticular material changes. In theory, a infinite number of frames can be interlaced with this process with each frame differing from its neighbors by minute changes in perspective. In practice, normally ten or more interlaced frames are used.
Lenticular autostereoscopic displays also achieve an animation sequence of images if a high number of interlaced source frames are used. However, the ability to show animation within normal lenticular displays requires an exceptionally high number of source frames to be used since each pair of frames must contain an image that has not moved to such a degree that stereoscopic perception of the image is unable to be achieved. Thus, lenticular autostereoscopic animation is limited in that the displacement of objects between any two adjacent or closely related frames must be sufficiently small or negligible, so as not to interfere with the stereoscopic viewing of the adjacent source frames.
Thus, autostereoscopic displays not containing the limitations of presently existing lenticular screen displays or stereo pair images is desired.